1. Field of the Invention
This invention relates to an improved apparatus and method for purifying a fluid product by removing certain components of a fluid mixture or contaminants from a source of a single fluid. Since this invention is effective in separation of gases and liquids, depending on circumstances, the term fluid will be used as much as possible. It is understood that the term includes gases and liquids. Although focus is directed to the medical use as a respiratory support in the present embodiment, this invention is also useful in other situations where zeolites and sieve materials are employed, for example oil refinery procedures.
2. Description of the Related Art
The use of selectively adsorbent molecular sieve materials having uniform pore sizes in separation of fluid components has been in practice since about 1948, with the first industrial research efforts occurring at Union Carbide Corporation. Based on the first experimental observations of the adsorption of gases on naturally occurring zeolites and the behavior of the latter as molecular sieves by Barrer in 1945 (J. Soc. Chem. Ind., 64:130), Milton and coworkers at Union Carbide synthesized the first industrial zeolite molecular sieves in 1948 (R. M. Milton, Molecular Sieves, Soc. Chem. Ind., London, 1968, p. 199), and they were test marketed in 1954.
Most separations of fluid mixtures by adsorption require regeneration of the adsorbent after saturation with the adsorbate. Since most separations are performed on fixed-bed columns, complex mechanisms involving intricate networks of interconnected and interoperating valves and switches have been devised to implement adsorption and desorption cycles in order to facilitate regeneration.
Costly and elaborate equipment like that described above is suitable for large scale commercial operations where the equipment is constantly monitored by competent technicians. However, in dealing with the problem of supplying relatively small quantities of oxygen to patients, especially at home, size, ease of operation and, even more importantly, reliability are the primary concerns.
The use of synthetic molecular sieves in a two-bed, pressure swing adsorber for separation of oxygen from air for medical and industrial applications became commercially practical in the early 1970's and many manufacturers build such equipment.
The components in a typical two column system currently available are:
Air compressor PA1 Heat exchanger PA1 Air receiver or surge tank PA1 Two molecular sieve chambers PA1 Two pressure dropping orifices PA1 Product tank (oxygen receiver) PA1 Four or five two-way solenoid operated directional flow control valves (or, alternatively, one 4-way valve and one 2-way valve) PA1 Electrical or electronic sequencing timer control for the valves PA1 Pressure reducing regulator for oxygen product flow PA1 Intake and exhaust silencers PA1 Intake and product filters PA1 Adjustable flow control valve for oxygen product PA1 Connecting tubing and fittings to conduct fluid flows into and out of components
The above list of components clearly indicates the complexity of a typical medical oxygen concentrator respiratory support system), requiring a network interconnected parts acting in concert. This complexity can give rise to the prospect of decreased reliability, and the chance that some component will malfunction, or a connection leak will develop, rendering the entire apparatus incapable of performing its life-support function.
The compressor discharge profile in a two column system, when plotted against time manifests a "sawtooth" pattern which is responsible for shortening compressor valve and bearing life, requiring an air receiver or surge tank to limit such fluctuation. This cyclic flow in the two column adsorber also produces large pressure variations in product gas flow, requiring the use of a pressure reducing regulator in the dispensing conduit. The abrupt, large pressure changes also require extensive silencing.
Furthermore, to provide an ambulatory patient with acceptable mobility and quality of life, a supplementary oxygen supply system must be reliable, economical, compact, portable and light in weight. The instant invention provides a system which addresses all these parameters.